I'd wager that the child in the picture has leukemia and his chubbyness is the result of cortical steroids being fatistered to negate the effects of chemo treatment. I find it difficult to believe that this body type could arise from such poor diet, alone, at such a young age. Loss of appetite is a common side effect of chemotherapy and this can be detrimental to a child's growth if he/she isn't receiving adequate nourishment. The steroids fatistered induce appetite (often they still won't eat much) and accelerate cellular metabolism so that the child can still grow while fighting the cancer.

TL;DR: Boy is fat, but most likely eats very little. If I'm wrong, he's just training to be sumo champ.